Noam Shapiro | InZiv: Is your photoluminescence (PL) inspection giving you false confidence in your microLED yield?
00:06:12 - 00:07:33
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Summary of the clip:
Is your photoluminescence (PL) inspection giving you false confidence in your microLED yield?
The problem with photoluminescence (PL) is that it can misrepresent the true performance of a microLED. This clip shows a direct, side-by-side comparison of the same microLED chip tested with both PL and electroluminescence (EL). The resulting topographical images reveal a stark difference in the measured defective area, highlighting a fundamental flaw in relying on optical excitation for quality control.
Under PL, the non-emissive, defective region appears smaller than it actually is. When the same chip is driven electrically via EL—mimicking its real-world operation—the defective area is visibly larger. This discrepancy leads to a "false positive," where a chip that would fail in a final display is passed during initial wafer-level screening, ultimately poisoning the downstream manufacturing process and lowering final yields.
Beyond just identifying dead zones, PL also fails to accurately predict the light output intensity. The process of optical excitation in PL does not replicate the carrier injection and recombination dynamics of electrical excitation. As a result, the intensity map generated by PL can be a poor predictor of the chip's actual luminance and uniformity under operational conditions, which are critical for display quality.
In this short video, you can learn:
* The visual evidence of PL providing "false positives" on microLED defects.
* Why EL reveals a larger, more accurate defective area than PL on the same chip.
* How PL provides an inaccurate prediction of a microLED's final light intensity.
📋 **Clip Abstract** Photoluminescence (PL) testing can be a dangerously inaccurate predictor of microLED performance, often underestimating the size of defective areas. This direct comparison with Electroluminescence (EL) shows why PL can lead to false positives, passing faulty chips that will ultimately reduce display yield.
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#MicroLEDYield, #PLvsEL, #MicroLEDDefectDetection, #DisplayQualityControl, #ARdisplays, #AdvancedDisplayMetrology
This is a highlight of the presentation:
Unleashing microLED’s Future: The Power of Electroluminescence Testing
MicroLEDs, AR/VR Displays, Micro-Optics 2025: Innovations, Start-Ups, Market Trends
Online | TechBlick platform
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TechBlick
MicroLED Connect
More Highlights from the same talk.
00:08:31 - 00:10:01
Think you can just calibrate your fast PL measurements to predict EL performance? This data suggests otherwise.
Think you can just calibrate your fast PL measurements to predict EL performance? This data suggests otherwise.
A common strategy to leverage the speed of photoluminescence (PL) is to attempt to create a correlation model that maps PL results to the more accurate electroluminescence (EL) data. However, this clip presents compelling evidence from a university study that demonstrates the fundamental inconsistency of PL, making such a correlation unreliable. The study analyzed two microLED chips produced under the exact same epi-wafer and fabrication recipe.
When measuring the peak emission wavelength, the EL results for both Chip A and Chip B were virtually identical, showing process consistency as expected. In stark contrast, the PL measurements for the same two chips showed a significant shift in peak wavelength relative to each other. This demonstrates that subtle, inevitable process variations can affect PL and EL results differently, breaking any simple correlation.
The core issue is the lack of a consistent pattern or predictable offset between PL and EL measurements across different chips, even from the same batch. Because the PL data shifts unpredictably while the EL data remains stable, it's impossible to establish a reliable calibration factor. This invalidates the use of PL as a fast proxy for EL, as the results cannot be trusted to reflect true device performance for binning or quality control.
In this short video, you can learn:
* Why creating a simple correlation between PL and EL data is not feasible.
* Data showing how two identical microLEDs can have stable EL wavelengths but shifting PL wavelengths.
* The impact of process variations on the consistency of PL measurements, making them unreliable for prediction.
📋 **Clip Abstract** This clip debunks the idea of using a simple calibration to make fast PL testing predict accurate EL results. Data shows that even on identically produced microLEDs, PL measurements are inconsistent and do not correlate reliably with stable EL performance, making PL an untrustworthy proxy.
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#MicroLEDs, #Photoluminescence, #Electroluminescence, #DeviceCharacterization, #ARdisplays, #DisplayTechnology
00:10:01 - 00:11:25
Why is your microLED display's brightness uniformity so poor? Your PL inspection is blind to the root cause.
Why is your microLED display's brightness uniformity so poor? Your PL inspection is blind to the root cause.
A critical deficiency of photoluminescence (PL) is its complete inability to provide electrical information, as it uses optical rather than electrical excitation. This clip highlights the danger of this data gap by showing an IV (current-voltage) curve analysis of multiple microLED chips from a single wafer. The results reveal significant electrical non-uniformity that PL inspection would completely miss, which is a primary driver of poor display quality.
The IV plot demonstrates that when the same voltage is applied to different microLEDs, they can draw vastly different amounts of current. This variation in the forward voltage (Vf) is a critical performance parameter. Chips with different Vf characteristics will have different brightness levels and efficiencies when driven by a common backplane voltage, leading directly to poor display uniformity, also known as mura.
The ramifications of this electrical variation are severe, impacting not only brightness uniformity but also power consumption and device lifetime. Imbalanced voltages and currents across pixels can cause differential aging, leading to burn-in and reduced display lifespan. Only electroluminescence (EL) testing, which directly measures the IV curve of each chip, can capture this vital data needed for binning, sorting, and process feedback to improve uniformity.
In this short video, you can learn:
* The fundamental inability of PL to measure crucial electrical properties like the IV curve.
* How IV curve variations across a single wafer directly cause brightness non-uniformity (mura).
* The long-term impact of electrical non-uniformity on display lifetime and power efficiency.
📋 **Clip Abstract** Photoluminescence (PL) is blind to the electrical variations between microLEDs, a critical factor for display quality. This clip explains how only Electroluminescence (EL) can measure IV curves, revealing forward voltage non-uniformity that directly causes mura, impacts power efficiency, and reduces display lifetime.
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#MicroLEDDisplays, #ELTesting, #IVCurveAnalysis, #DisplayMura, #ARDisplays, #AdvancedDisplays